Absorbent articles for personal hygiene, such as disposable baby diapers, training pants for toddlers or adult incontinence undergarments, are designed to absorb and contain body exudates, in particular large quantity of urine. These absorbent articles comprise several layers providing different functions, for example a topsheet, a backsheet and in-between an absorbent core, among other layers.
The function of the absorbent core is usually to absorb and retain the exudates for a prolonged amount of time, minimize re-wet to keep the wearer dry and avoid soiling of clothes or bed sheets. The majority of currently marketed absorbent articles comprise as absorbent material a blend of comminuted wood pulp with superabsorbent polymers (SAP) in particulate form, also called absorbent gelling materials (AGM), see for example U.S. Pat. No. 5,151,092 (Buell). Absorbent articles having a core consisting essentially of SAP as absorbent material (so called “airfelt-free” cores) have also been proposed (see e.g. WO2008/155699 (Hundorf), WO95/11652 (Tanzer), WO2012/052172 (Van Malderen)). Absorbent cores with slits or grooves have also been proposed, typically to increase the fluid acquisition properties of the core or to act as a folding guide. WO2009/047596 (Wright) discloses an absorbent article with a slit absorbent core.
US2004/220541 (Suzuki) discloses an absorbent sheet having concave and convex portions on its surface and spontaneously exhibiting a three-dimensional structure in that a concave-convex structure is formed. US2007/244455 (Hansson) discloses an absorbent core in an absorbent article provided with at least two folding guides extending in a substantially longitudinal direction in the crotch region and dividing at least a part of the crotch region of the absorbent core in a central portion and two lateral portions as seen in a transverse direction. At least two stretchable crotch elastic members are arranged in the crotch portion of the article and are attached to the absorbent core and/or to the inner or outer cover.
It is also known to provide a sub-layer, typically a nonwoven, between the topsheet and the absorbent core. These sub-layers are designed to quickly acquire and/or distribute the fluid away from the topsheet and into the core. These sub-layers are sometimes called “wicking layer”, “surge layer”, “acquisition layer” or “distribution layer”. Articles having only one of these sub-layers are known. A single sub-layer is disclosed for example in WO94/23761 (Payne), which discloses an acquisition layer comprising an homogeneous composition of hydrophilic fibrous material and a storage layer comprising a mixture of hydrophilic fibrous material and discrete particles of absorbent gelling material. The acquisition layer has an acquisition zone towards the front of the article of relatively lower average density and relatively lower average basis weight than a distribution zone towards the back of the article. Another example of sub-layer having a single layer can be found in U.S. Pat. No. 5,486,166 and U.S. Pat. No. 5,490,846 (Bishop).
US2008/0312621 and US2008/0312622 (Hundorf) describe a disposable absorbent article comprising a chassis including a topsheet and a backsheet, a substantially cellulose free absorbent core located between the topsheet and the backsheet and having a wearer facing side oriented toward a wearer when the article is being worn and an opposed garment facing side, and a “liquid acquisition system” comprising chemically cross-linked cellulosic fibers disposed between the liquid permeable topsheet and the wearer facing side of the absorbent core. The liquid acquisition system may also comprise an upper acquisition layer made of a latex bonded nonwoven.
WO2012/170778 (Rosati et al., see also WO2012/170779, WO2012/170781 and WO2012/170808) discloses absorbent structures that comprise superabsorbent polymer, optionally a cellulosic material, and at least a pair of substantially longitudinally extending channels. The core wrap can be adhesively bonded through the channels to form a channel bond. The channel bonds may be permanent, so that their integrity is at least partially maintained both in dry and wet state. As the absorbent structure absorbs liquid and swells, the absorbent structure takes a three-dimensional shape with the channels becoming visible. The channels provide improved fit and/or liquid acquisition/transportation, and/or improved performance throughout the use of the absorbent structure.
In a first aspect of the invention, the inventors have now found that the formation of three-dimensional channels in a wet absorbent core can help forming three-dimensional ditches in a fibrous structure placed between the topsheet and the topside of the absorbent core. The fibrous structure may for example be an acquisition and/or a distribution layer. The ditches in the fibrous layer can provide advantages in term of fluid acquisition and distribution. In a second aspect, the invention is for an absorbent core that can be used in the article of the invention and that comprises a core wrap bond that gradually open as the absorbent core swells to provide additional swelling space for the swollen absorbent material.